Existing beacon technology provides navigation and location reference points to assist a device in determining its own position or location. Beacons based on Infrared (“IR”), BlueTooth®, Wi-Fi access points, Global Positioning System (“GPS”) satellites, Quick Response (“QR”) codes, Ultra-WideBand (“UWB”) time-of-flight and magnetic field contour maps are all used as known reference points to inform a device (such as a mobile phone) of its own location. Systems deriving fine-grid location with little or no reliance on GPS are commonly referred to as Location Based Services (“LBS”) or Indoor Positioning Systems (“IPS”). These systems are used to infer location of other objects that are known to be nearby. For example, if a device is determined to be at position x, then an object that is known to be within a distance of y units of the located device is inferred to be within y units of position x. These systems require interaction with the device being located and are not suitable for integration with Radio Frequency Identification (“RFID”) tags.
Triangulation techniques are used to determine the position of another object based on information collected by observations of the object from one or more known locations. Cellular triangulation, Wi-Fi triangulation, and various land survey techniques all collect information (such as direction to the object and/or signal strength from the object) from one or more reference positions and derive an approximation of that object's location. This requires having multiple observation points with known positions. The wider the area of unknown objects, the greater the number of observation points is needed to achieve a given accuracy.
Passive RFID is widely used for inventory assessment, providing an RFID reader with information about an RFID tag's presence but little in the way of the RFID tag's position beyond broad direction and signal strength information from which approximate locations might be inferred. Often, an RFID tag is read correctly but the derived direction and signal strength information are corrupt due to multi-path and antenna side-lobe distortions. The wide beamwidth of the RFID reader's antenna limits directional precision. The orientation of the RFID tag's antenna relative to the RFID reader's antenna has a similar influence on the Received Signal Strength Indicator (“RSSI”) as distance has, i.e., a close RFID tag turned sideways to the RFID reader can have a lower returned signal than a distant RFID tag with a favorable orientation toward the RFID reader. This potential for distance inversion limits the value of RSSI in determining actual position of an RFID tag based on a single tag read.
Arrays of antennas with RFID readers provide finer resolution but scale poorly, are expensive, difficult to deploy and difficult to change. Use of beam-steered antennas such as the Impinj X-Array and Sensormatic IDSM-1000 and IDA-3100 can be configured to provide relative angle of the RFID tag to the antenna or RFID tag position/location at a chokepoint.